Plastic zinc alloy of constant dimensions



Patented July 18,1939

UNITEDYSTATES PATENT OFFICE.

PLASTIC ZINC ALLOY or CONSTANT DIMENSIONS Arthur Burkhardt, Berlin-Lichterfelde, Germany, assignor to Georg von Giesches Erben, Breslau, Germany, a corporation of Germany No Drawing. Application October 25, 1937, Se-

rial No. 170,853. In Germany November 6,

4 Claims.

My invention relates to plastic zinc alloys containing aluminium and copper, and, if desired,

a small percentage of magnesium.

It is an object of my invention to provide an 5 alloy of the kind described which possesses a constancy of dimensions heretofore unat d (c1. va-ns) any dimensional change, even after long continued artificial ageing at 95 centigrade.

By way of example, alloys embodying my invention may have the following compositions in in any alloy of the type described.

To this end, in an alloy having a copper content of 2 to 8 per cent, i so determine the content of aluminium that it corresponds to the proportion of 18 to 22 parts of copper to 1 part per than when in the same condition at room temperature. The consequence is that during the cooling of the alloy after its production, or after, a treatment carried out at elevated temperature, certain quantities of aluminium and 25 copper separate out.

The separation produces a. change in the properties of, the alloy by which its strength is reduced and its dimensions are varied.

The change in dimensions is particularly inconvenient in practice since it is difierent in parts of various sizes and sections. If such parts are to be assembled, this necessitates much fitting work.

It was not known heretofore that the influence of the separation on the dimensions is diiierent in extruding and in casting alloys.

In extruding alloys, the separation of aluminium results in an increase in length, and that of, copper in a shrinkage. In casting alloys, the influence of the two constituents is the reverse. According to the composition of the alloys and to the degree of supersaturation, the dimensional changes are more or less considerable.

45 I have made the surprising discovery that by suitably selecting the content of copper and aluminium the increase in length and the shrinkage canbe so determined that they compensate one another.

It has been found that only alloys in which the content of copper is 2 to 8 per cent, and the proportion of aluminium to copper is between 1 to 18 and 1 to 22, possess absolute constancy of dimensions. Thus, alloys in which the said proportion is 1 to 20, were found not to exhibit per cent:

' Copper Aluminum 1 2 0.1 2 4 0.2 a c 0.3 4 s 0.4

The remainder in all cases is zinc of high purity, at least 99.99 per cent.

It is advisable that the percentage of aluminium in such alloys should not be under 0.1 per cent, as otherwise they attack iron strongly in molten'conditionand must not be melted in iron containers.

If the content of copper is exceeded, i. e., if the alloy contains more than 8 per cent copper, it is constant in dimensions but loses some of its good mechanical properties on ageing. This even occurs to some extent with the maximum content of 8 per cent copper.

grammes per square millimeter. vary only very slightly upon ageing.

These values On the other hand, in an extruding alloy having 8 per cent copper and 0.4 aluminium, (4) of the above table, the tensile strength is as high as 41 to 43 kilogrammes per square millimeter, the elongation is only 5 to 10, the reduction in area is 20 to 30 per cent, and the impact bending strength is 8 to 12 centimeter kilogrammes per square millimeter, in the initial condition of the alloy. After ageing, this alloy still possesses absolute constancy of dimensions but its tensile ,strength is only to 37 kilogrammes per square millimeter, the elongation is 3 to 6 per cent, the reduction in area is 10 to 20 per cent, and the impact bending strength is 2 to 5 centimeter kilogrammes per square millimeter.

- An addition of small quantities of magnesium in the limits of 0.03 to 0.1 per cent has a favorable eflect on the tensile strength which is increased tor about 10 per cent while, on the other hand, the-elongation drops to about half the value of the alloy without magnesium.

By way of example, 0.05 per cent magnesium may be added to any one of the alloys in the above table.

Zinc alloys for die casting are known which, besides copper and aluminium, contain a small percentage of magnesium. But in these known die-casting alloys no importance was placed on the observance of a strictly limited proportion of aluminium to copper, since it had not been recognised that by such observance it is possible to produce alloys which are constant in dimensions.

Nor had it been recognised that aluminium and copper, as stated above, behave differently with respect to dimensional change in extruding I and in die-casting alloys.

A further advantage of my new alloys over the customary extrusion alloys is their higher extrusion velocity. Thus, while with the customary extrusion zinc alloy containing 0.5 to 2.5 per cent copper and 4 per cent aluminium, the extrusion velocity is 2 meters per minute, it may be increased to '7 meters per minute with my new alloys.

I claim:

1. A plastic zinc alloy containing 2to 8% copper and about 0.09 to about 0.45% aluminum, the contents of' copper and aluminum having a mutual proportion of 18 to 22 parts of copper to 1 part of aluminum, the remainder zinc.

2. A plastic zinc alloy containing about -l:% copper and about 0.18 to about 0.22% aluminum, the remainder zinc.

3. A plastic zinc alloy containing 4% copper and 0.2% aluminum, the remainder zinc.

4. A plastic zinc alloy containing 2 to 8% copper and 0.1 to 0.4% aluminum, the remainder zinc.

ARTHUR BURKHARD'I'. 

